The normal function of the mammalian kidney includes such activity as maintaining a constant acid-base and electrolyte balance, removing excess fluids and removing undesirable products of the body's metabolism from the blood. Heretofore, dialysis methods such as hemodialysis and peritoneal dialysis have been practiced on patients whose kidney function was reduced. Here, in hemodialysis, the blood is withdrawn from the patient's bloodstream and passed through a dialyzer wherein the blood is brought into contact with a selectively permeable membrane made, for example, of cellulosic acetate, the remote side of which contacts a dialysis fluid. By a principle of diffusion, solutes in the blood are transported across the membrane into the dialysis fluid and water is removed by ultrafiltration. The treatment is normally carried out in the out-patient department of hospitals but causes patients to be retained in the hospital for a long time.
Peritoneal dialysis is now a well-established procedure which may be substituted for extacorporeal hemodialysis and has an it advantage in that patients do not have to be treated in hospitals and the procedure can be carried out at home. The conventional peritoneal dialysis comprises introducing a fresh peritoneal dialysis fluid into a peritoneal cavity in the abdomen of the patient, allowing the fluid to remain there for several hours, dialyzing the fluids through a peritoneum as a semi-permeable membrane, and then draining the dialysis fluid containing metabolic waste products from the peritoneal cavity. However, this procedure has disadvantages including the problem and danger of peritonitis, a lower efficiency than hemodialysis which requires a longer treatment or process time with large volumes of solution and a high cost of commercially prepared dialysate solution.
Accordingly, in order to increase the efficiency of peritoneal dialysis, a number of improved peritoneal dialyses have been known.
In U.S. Pat. No. 5,141,493 there is disclosed a peritoneal dialysis system which comprises connection means for carrying a primary solution that is a peritoneal dialysis fluid from a primary circuit means to a peritoneal cavity of a patient, withdrawing at least some solution from the patient into the primary circuit means, wherein the primary circuit means has a reversible pump for circulating the primary solution, and a dialyzer to enable removal of waste products from the primary solution to a secondary solution that is a dialysate for hemodialysis. The peritoneal dialysis fluid withdrawn from the peritoneal cavity of the patient is purified sequentially with said dialysate through the dialyzer and returned again into the cavity of the patient.
In U.S. Pat. No. 5,641,405 there is disclosed a system including only one pump for providing a peritoneal dialysis fluid into and out of a patient. This system comprises a single catheter, a source of peritoneal dialysis fluid, a dialyzer and a single reversible pump positioned between the source of peritoneal dialysis fluid and the catheter. In this arrangement, the peritoneal dialysis fluid is passed from the source of peritoneal dialysis fluid through the dialyzer to be dialyzed before reaching the catheter and pumped out of the peritoneal cavity of the patient to the source of dialysis fluid and temporarily pooled in the source, and then passed through the dialyzer again and returned to the peritoneal cavity of the patient.
The peritoneal dialysis fluid used in the above-described two peritoneal dialysis systems contains glucose as an osmotic agent. Solutes such as urea and creatinine diffuse from the blood in capillaries of the peritoneum into the dialysis fluid due to the presence of a diffusion gradient. Also the presence of an osmotic gradient due to glucose between the peritoneal cavity and the blood causes excess water removal from the blood in the peritoneal capillaries into the dialysis fluid which is then drained outside the abdomen of the patient. However, glucose in the dialysis fluid permeates through the hollow fiber membrane of the extracorporeal dialyzer to be readily taken up into a dialysate as cleaning solution because the separation limitation of the membrane is approximately 5,000 to 10,000 daltons. Accordingly, there is a problem that in order to maintain the osmotic gradient which is a water-removing ability of the peritoneal dialysis fluid, glucose must be supplied into the fluid during the peritoneal dialysis using a glucose injector, etc. As for the usage of glucose, for example, when the peritoneal dialysis fluid is circulated at a flow rate of 0.1 liter/minute for 6 hours, while maintaining an osmotic pressure of 1.5% dialysis fluid, 15 g of glucose is contained in one liter of dialysis fluid : Daianeal 1.5 (trade name, manufactured by Baxter), a huge amount of glucose is necessary as shown by the following formula.0.1(liter)×60(min)×6(h)×15(g)=540(g)